Conventional fixed moulds have been used for many years for casting rectangular sheet ingots. Aluminum sheet is used in many different fields and there has been an increasing demand for sheet of different widths. This in turn has created an increasing demand for ingots of different dimensions.
In a direct chill casting system, aluminum or other molten metal is poured into the inlet end of an open-ended mould while liquid coolant is applied to the inner periphery of the mould to cool the mould walls and generate primary cooling. Also, the same or different coolant is normally applied as secondary cooling to the surface of the ingot as it emerges from the outlet end of the mould, to continue the cooling effect on the solidifying metal. The coolant is applied around the periphery of the mould or a portion thereof, as well as to the faces of the emerging ingot, to make the cooling effect as uniform as possible.
Because of the high coefficient of thermal expansion of aluminum, in order to obtain flat ingots, moulds have been devised which are capable of forming a crown on the longer side walls of a rectangular ingot to compensate for uneven wall distortion which these side walls experience as the ingot solidifies. Thus, the long walls of the rectangular mould are typically outwardly curved. A slight curvature may be imposed on moulds for casting steel, but it is substantially less than that required for metals such as aluminum.
Because of the relative complexity of the mould systems as described above and the fact that the walls of the mould also carry coolant, it will be recognized that it is not a simple matter to design such a mould assembly having adjustable side walls. Thone et al. U.S. Pat. No. 4,516,622 discloses a straight sided mould used for steel in which hydraulic cylinders can move the long walls with respect to the mould frame. The hydraulic cylinders are disposed symmetrically on either side of the centre line of the mould but they are unidirectional and are designed merely to clamp the side wall to the ends in use. Although the side walls are independent of the end walls, in fact the end walls are precisely fixed with respect to the mould centre line so that in use, the side walls become positioned with respect to the centre line by the action of the end walls.
Negishi, U.S. Pat. No. 5,146,975 describes a variable-width mould device for casting aluminum in which the long walls of the mould are outwardly curved. The end walls are held in position by sliding guides which contain water feeds. The side walls are attached to the end walls and therefore move in relationship to the movement of the end walls. The positioning of the side walls with respect to the bottom block is dependent on maintaining the end wall in position with respect to the bottom block, which requires no sideways flexibility in the connections between the moveable end walls and the frame.
It is the object of the present invention to provide a casting apparatus for casting metal ingots of rectangular shape in which both the opposed long (side) walls and opposed short (end) walls of the mould are easily and precisely moveable.